1. Field of the Invention
The present invention relates to a method of correcting image errors in the transmission of difference pulse code modulated (DPCM) coded image signals.
2. Description of the Prior Art
In the transmission of image signals, two fundamental methods are known for correcting image errors. in the first method, error-correcting codes are used to reduce transmission errors. However, these codes require a proportion of more than 5% of the transmission capacity. In the case of the second method, so-called image error masking is used. For this purpose, it is merely necessary to recognize a transmission error and to replace the adulterated image signal values by correction values which have been obtained from a preceding television image or by interpolation from the surrounding image signal values.
If image signals are transmitted by difference pulse code modulation, the adulteration of a single DPCM value is sufficient to produce a so-called error trail which adulterates the television image to a substantially greater extent than individual adulterated image signal values in the case of pulse code modulation (PCM) coding.